Quantifying the effects of seed arrival and environmental conditions on tropical seedling community structure

Abstract

Though it is recognized that both stochastic and deterministic processes structure all communities, empirical assessments of their relative importance are rare, particularly within any single community. In this paper, we quantify the dynamic effects of dispersal assembly and niche assembly on the seedling layer in a diverse neotropical rain forest. The two theories make divergent predictions regarding the roles of seed arrival and environmental heterogeneity in generating community structure. Put simply, dispersal assembly posits that the stochasticity inherent to seed arrival structures communities, whereas niche assembly suggests that heterogeneity in post-dispersal environmental conditions is more important. We experimentally sowed 15,132 seeds of eight tree species at varying levels of density and diversity. Every six months we censused the seedlings that germinated and assessed the abiotic and biotic conditions of each plot. We assessed the density, diversity, and species composition of three nested subsets , and all woody seedlings. We partitioned the variance in density and diversity of each subset of the seedling layer into components representing seed-addition treatments and environmental conditions at 6-to 12-month intervals. Seed additions initially explained more variance in the density and diversity than did environmental heterogeneity for seven of eight sown species, but explained little variance in the density or diversity of the entire seedling layer. Species composition was better explained by seed-addition treatments than by environmental heterogeneity for all three subsets and in all time periods. Nevertheless, the variance in community structure explained by seed-addition treatments declined over the two years following germination, presaging shifts in the relative importance of dispersal assembly and niche assembly. Our study quantifies how dispersal assembly and niche assembly may vary among the components of an ecological community and shift dynamically through time.

Natural Regeneration of Tree Species in a Cloud Forest in Santa Catarina, Brazil

“…PAINE; HARMS, 2009;HIGUCHI et al, 2015). According to Higuchi et al (2015), the natural regeneration process in a forest's understory starts with the arrival and subsequent germination of seeds on the forest floor, which, according to Guarigata and Pinard (1998), occurs in an irregular way.…”

Interspecific Functional Convergence and Divergence and Intraspecific Negative Density Dependence Underlie the Seed-to-Seedling Transition in Tropical Trees

“…Seedling and sapling studies have argued for the importance of negative density dependence (Harms et al 2000;Metz et al 2010), abiotic filtering , or stochastic survivorship (Paine and Harms 2009). However, it is more likely that all of these factors act at the same time (e.g., Swenson and Enquist 2009), making it important to disentangle their importance in structuring tropical tree communities through space and time.…”

“…There have been many temporally static investigations of seedling assemblages (Augspurger 1984;Nicotra 1999;Norden et al 2007;Paine et al 2012) and some dynamic investiga-tions of the seedling-to-sapling transition Green et al 2014), but there are few detailed forest-wide investigations of perhaps the largest demographic bottleneck of all: the seed-to-seedling transition (Harms et al 2000;Norden et al 2009;Paine and Harms 2009;Muscarella et al 2013). One of the best known of these investigations comes from Harms et al (2000), who found that the seed-to-seedling transition in a Panamanian tropical forest assemblage was strongly influenced by negative density dependence.…”

Seedling recruitment factors in low‐diversity Hawaiian wet forest: towards global comparisons among tropical forests

“…For example, high seed limitation is an ''equalizing'' mechanism that may promote species coexistence by allowing species to avoid hierarchical interspecific competition (i.e., ''winning-by-forfeit''; Hurtt and Pacala 1995). Alternatively, high establishment limitation reflects niche differentiation and habitat specificity which are ''stabilizing'' mechanisms for species coexistence (Tilman 1994, Chesson 2000, MullerLandau et al 2002, Gravel et al 2006, Adler et al 2007, Paine and Harms 2009, Mutshinda and O'Hara 2011.…”